Local Bonding Influence on the Band Edge and Band Gap Formation in Quaternary Chalcopyrites

Abstract

Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu2ZnGeS4− xSex, the anion bond alteration parameter changes, showing larger bond lengths for metal–selenium than for metal–sulfur bonds. The changing bonding interaction directly influences the valence and conduction band edges, which result from antibonding Cu–anion and Ge–anion interactions, respectively. The knowledge of the underlying bonding interactions at the band edges can help design properties of these quaternary chalcopyrites for photovoltaic and thermoelectric applications.

Structural, Topography, and Optical Properties of Ba‐Doped Mn3O4 Thin Films for Ammonia Gas Sensing Application

“…The band gap of the sprayed films is calculated using Tauc's relation using the following equation: where α , B , and Eg are the absorption coefficient, proportionality constant, and optical band gap; respectively, the absorption coefficient is calculated by the following equation: where A and t are the absorbance and thickness, respectively, Figure shows the band gap of pure and Ba‐doped Mn 3 O 4 thin films, the values fairly agree with the work reported in literature . It is found that band gap varies as Ba concentration increases reaching a minimum value 2.85 eV in Mn 3 O 4 :Ba1% thin films, the reduction in band gap may be due to the increase in RMS roughness and crystallite size as reported earlier, it is also observed band gap decreases with the increase in unit cell volume as well as bond lengths of (Mn 2+ O) and (Mn 3+ O) in tetrahedral and octahedral sites; respectively (see Table ) as Ba concentration increases, this behavior agrees with the findings reported in literature …”

Unequal bonding in Ag–CuIn3Se5-based solid solutions responsible for reduction in lattice thermal conductivity and improvement in thermoelectric performance

“…3 and 4b), as was the cases in the solid solutions Cu 2 -ZnGeS 4Àx Se x (ref. [39][40][41] or Cu 2Àx Se. 42 The existence of the repelling force upon Ag incorporation can be supported by the analyzed Raman spectra (shown in Fig.…”

Regulation of the Crystal Structure Leading to the Bandgap Widening and Phonon Scattering Increasing in Cu3SnS4‐Cu3SbSe3 Chalcogenides

“…The panel (c‐g) in Figure represent the plots of ( A.hν ) 2 versus photon energy ( hν ) for different x values. The widening of the bandgap can be ascribed to the reduction of p‐d hybridization caused by weakened CuS bond interaction . The calculated E g values are smaller than those experimentally determined (1.05–1.51 eV) as a result of GGA problem, while the latter ones are comparable to 1.21 eV from the synthesis in solvent .…”

“…Inspired by the influence of bonding interactions on the band structures and phonon transport property observed in quaternary Cu 2 ZnGeQ 4 (Q = S, Se), we take underlying crystal and electronic structure regulations in Cu 3 SnS 4 into consideration. Due to the small difference of radius and electronegativity between Sn 4+ (0.55 Å, 1.96) and Sb 5+ (0.565 Å, 2.05), Sb is presumably energetically favorable to Sn site.…”

“…The cation substitution changes the bond interaction, thus directly affecting the p‐d hybridization . Besides, as element Se is slightly more electronegative, the residing of Se at S site also intuitively increases the bond length which results in an increase in the bandgap and a broader valence band dispersion . In the meantime, the hybridization of Cu d ‐Se p (or Sb p –Se p ) orbital or the formation of conducting bond network CuSe tends to contribute the DOS near the Fermi level (E f ) and, subsequently, promotes the transport of carriers .…”